The present invention relates to a distribution-type fuel injection system controlled by an electromagnetic valve.
A fuel injection system employing a distribution-type fuel injection pump controlled by an electromagnetic valve is known as one of fuel injection systems for use in diesel engines.
The distribution-type fuel injection pump comprises a housing having a low-pressure chamber defined therein. A plunger barrel is mounted to the housing. A plunger is fitted in the plunger barrel for axially reciprocative movement and for rotation relative to the plunger barrel.
A fuel pressurizing chamber is defined by an end face of the plunger and an inner peripheral surface of the plunger barrel. Forward movement of the plunger reduces the volume of the fuel pressurizing chamber, while backward or return movement of the plunger increases the volume of the fuel pressurizing chamber. During one revolution of the plunger, the plunger reciprocates several times corresponding in number to cylinders of the engine. At the forward strokes of the plunger, the fuel pressurizing chamber is brought into communication successively with fuel injection valves of the engine through a passage formed in the plunger, a plurality of ports formed in the plunger barrel, a plurality of passages formed in the housing and a plurality of delivery valves.
The fuel pressurizing chamber communicates with the low-pressure chamber through a relief passage formed in the housing The relief passage is adapted to be opened and closed by the electromagnetic valve. Fuel is permitted to escape from the fuel pressurizing chamber to the low-pressure chamber through the relief passage, for a period of time within which the electromagnetic valve is opened, during each forward stroke of the plunger. On the other hand, for a period of time within which the electromagnetic valve is closed during each forward stroke of the plunger, the fuel is supplied to a corresponding one of the engine cylinders from the fuel pressurizing chamber through a corresponding one of the fuel injection valves.
Accordingly, if a closing starting point of the electromagnetic valve is controlled, fuel injection starting timing can be controlled, while if an opening starting point of the electromagnetic valve is controlled, fuel injection termination timing can be controlled.
The electromagnetic valve is controlled by drive pulses outputted from a control circuit. That is, a starting point and a termination point of each drive pulse are determined in accordance with the engine running conditions, and the electromagnetic valve is closed in response to the drive pulse.
The electromagnetic valve operates in response to the drive pulse with a delay. Japanese Patent Application Laid-Open Nos. 61-286716 and 61-268844 disclose a system which comprises the above-mentioned fundamental arrangement and, in addition thereto, means for compensating for a delay in the fuel injection start-up and/or a delay in the fuel injection termination due to the delay in operation of the electromagnetic valve. Specifically, in the system, the delay time in the fuel injection start-up and/or the delay time in the fuel injection termination are/is detected with respect to the starting point and/or the termination point of the drive pulse, and the starting point and/or the termination point of the drive pulse are/is advanced correspondingly to the detected delay time or times.
The system disclosed in the above Japanese patents compensates for the delay time in the injection start-up and/or the delay time in the injection termination each time the fuel is injected into each cylinder, on the assumption that the delay times in the respective operations of the electromagnetic valve with respect to the engine cylinders are equal to each other. That is, the drive pulse is outputted by the control circuit in such a manner that the delay time or times detected at the fuel injection operation with respect to one cylinder is or are compensated for at the fuel injection operation with respect to the subsequent cylinder.
In practice, however, the delay times in the respective fuel injection operations of the electromagnetic valve with respect to the cylinders are different from each other. Accordingly, it is inevitable for the system disclosed in the above Japanese patents that variation occurs in the fuel injection starting timings and/or in the fuel injection termination timings for the respective cylinders.
The reason why the operation delay times in the electromagnetic valve are different from each other for the respective cylinders in spite of the fact that the electromagnetic valve is common to the cylinders is as follows. That is, because of processing errors of the delivery valves and because of a difference in position among the ports formed in the plunger barrel, the pressure within the fuel pressurizing chamber varies depending upon the fuel injection operations of the fuel injection pump with respect to the respective cylinders. Thus, the fuel pressure acting upon a valve member of the electromagnetic valve and flow of the fuel relative to the valve member vary delicately.
The above Japanese Patent Application Laid-Open No. 61-286716 corresponds to U.S. Pat. No. 4,748,447, and Japanese patent application Laid-Open No. 61-268844 corresponds to U.S. Ser. No. 865,125 filed on May 20, 1986.
Apart from the above, Japanese Patent Application Laid-Open No. 56-141026 discloses a distribution-type fuel injection system in which engine rotational speeds corresponding to expansion strokes of respective pistons within engine cylinders are detected to control an electromagnetic valve in such a manner that the rotational speeds are brought into coincidence with each other.
Japanese patent application Laid-Open No. 53-99134 discloses a fuel injection system which is different from that of distribution type, but which comprises means for compensating for a delay in closing operation of an electromagnetic valve.